Hello
OK465;
The question might rather be, "Will the THS move WITHOUT a change in airspeed along the instantaneous flight path, regardless of SS command?"
No, the design would not permit this.
The THS can be moved any time using the mechanical system, controlled by the two trim wheels on either side of the thrust lever quadrant.
The THS will not move under electronic control (sidestick or AFS request) unless commanded by the FCPCs. When the THS reaches the FCPC-commanded position the electronic control stops the hydraulic motor.
Operation/Control and Indicating
There are three control modes for the THS:
- autoflight (electrical control)
- manual (electrical control)
- standby (mechanical control)
In the autoflight mode the command signals from the autopilot are sent to the FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator.
In the manual mode the command signals from the side sticks are sent to the FCPCs. The FCPCs transmit autotrim signals to the electric motors which control the THS actuator.
In the standby mode the command signals are transmitted mechanically from the control wheels to the override mechanism. The override mechanism cancels the autotrim signals from the FCPCs. It transmits the mechanical command signals directly to the hydraulic motors of the THS actuator. Maximum Operating Load and Associated Maximum Speed (one motor):
18940 daN (42578.81 lbf) 0.2⁰ per second
16950 daN (38105.11 lbf) 0.5⁰ per second
6770 daN (15219.56 lbf) 0.6⁰ per second
Multiply the values by two for two-motor operation
Maximum operating speed is limited by the PTA in the electrical mode to 1 degree per second.
A different way of looking at the
THS - Elevator operating relationship is to consider the Lockheed L1011's design. The L1011 did not have elevators or a THS. The entire horizontal stabilizer was the "elevator" and was full-time trim. I no longer have my L1011 FCOM so I can't describe how the trim was calculated when in autoflight but in manual flight, which we did all the time back then, trim was controlled by a small thumb-wheel on the control wheel. When flying manually one could gently tweak the trim as speed changed, otherwise one left the trim alone.
The point is, the THS on an aircraft is a "follow-up" concept, trimming out control forces and satisfying elevator demand, (and making full elevator available at all speeds...QED!). To put it pedantically I suppose, the role of the THS is not in the same category as a primary flight control.
We could think of the THS as "long-term" control and the elevator as "short-term", (I know you know this but for the benefit of those who may not immediately see the difference I include this simple clarification).
General arrangement of the A330 THS control system:
Mechanical trim wheel thrust lever quadrant arrangement:
